The asynchronous telecommunication mode is widely used and known in the telecommunication field. The design of telecommunication equipment operating in asynchronous mode has been made easier since the development and the wide marketing of specific components known as Serial Communication Controllers (SCCs), such as the SIGNETICS SCN26562. Such components provide full management of an asynchronous link with the desired transmission characteristics, namely speed, parity and the actual number of data bits per character.
A typical example of the use of such a Serial Communication Controller (SCC) is illustrated in FIG. 1 where there is depicted an asynchronous link between a Data Terminating Equipment (DTE) 1 and Data Circuit Terminating Equipment (DCE) 10 including an SCC 20 controlled by a microprocessor 11 associated with RAM storage 13, PROM storage 12 and I/O devices 15. The DCE can be used for allowing the connection of DTE 1 to local communication controller equipment.
The success of asynchronous telecommunication transmission in general, and the wide variety of equipment used in the telecommunication field have resulted in many characteristics being handled by SCC's.
The speed which is most often used in currently marketed DTE's generally has one of the following values: 75, 300, 600, 1200, 1800, 2400, 4800, 9600, 19200 bauds. The parity is selected to be an EVEN parity mode, an ODD parity mode or a NO PARITY mode. With respect to the number of bits per character, the transmission generally uses 6, 7 or 8 bits per character.
It therefore appears that numerous asynchronous transmission characteristics are used in the telecommunication field and communication between transmitting and receiving equipment will require that the same characteristics be used by each. The adaptation of one DCE to the characteristics of a given DTE generally requires intervention of an operator during the installation on both transmitting and receiving equipment.
An automatic setting of the speed and parity characteristics known as Autobaud exists in the prior art. It is based on the analysis of the first characters received from the DTE. In the AUTOBAUD method, the operator transmits a predetermined sequence of three characters, known to the asynchronous adapter. The three characters are usually "CR" (Carriage Return) , ".", "CR". The receiving equipment, which is set to predetermined speed and parity characteristics, analyzes the received sequence of characters and derives therefrom appropriate speed and parity characteristics to be used so that the following transmission will be correctly received.
Existing practice consists of using the first character "CR" to determine the speed at which the DTE is sending characters. The following two characters, i.e. ".", "CR" are then used to derive the parity characteristics, but this only works it the number of data bits per character which are used by the transmitting and the receiving devices are identical.
Accordingly the known AUTOBAUD system operates only when the transmitting and receiving devices use the same number of bits per character. A manual operation for setting all the characteristics of the asynchronous transmission, speed, parity, and number of bits per character is still required otherwise. Providing for automatically setting all asynchronous transmission parameters has long been desired in the telecommunication field.